A171579 - OEIS

A171579

Number of fixed polyominoes in equilibrium; a fixed polyomino is in equilibrium when its center of mass is vertically aligned with a cell with minimal coordinate.

%I #4 Jan 14 2013 04:55:10

%S 0,1,1,2,5,12,27,70,192,589,1825,5870,18952,62997,211014,718474,

%T 2468741,8578400

%N Number of fixed polyominoes in equilibrium; a fixed polyomino is in equilibrium when its center of mass is vertically aligned with a cell with minimal coordinate.

%e For n=3, we have 2 fixed polyominoes in equilibrium: namely the vertical 3-omino and the horizontal 3-omino, thus a(3)=2.

%Y Cf. A001168

%K hard,more,nonn

%O 1,4

%A Mark Elduck (mark.elduck(AT)gmail.com), Dec 12 2009, Dec 20 2009, Dec 21 2009